There is a need for aircraft-mounted reconnaissance cameras having wide angle capability for recording information from a relatively wide swath of the ground over which the aircraft passes. Conventionally such cameras have utilized photographic film and known lensing techniques.
A charge-coupled device (CCD) one dimensional array has been utilized with the array oriented cross-track, i.e. at substantially right angles, to the direction of flight. Conventionally available CCD arrays comprise only a few hundred elements, although several thousand elements are necessary to provide the combination of acceptable resolution and wide angle capability. Several arrays are placed end to end to provide a desired resolution and wide angle capability. Associated with each array is a separate imaging lens, each lens being of a different focal length. The combination of lenses and arrays is such that the arrays are optically abutted. That is, a point on the ground which is adjacent to a point to be imaged on the last element of an array, n, will be imaged on the first element of the next array, n+1. The hardware for accomplishing this task is complex and costly. Further, after a given segment of the ground is imaged on the CCD array, the electronic signals contained therein must be quickly translated along and out of the arrays to some storage or other utilization device so that successive segments of the ground may be imaged on the arrays if acceptable along-the-track resolution is to be achieved. Thus, the lenses must be capable of passing a given amount of light to the array in a relatively short time, which requires the lenses to have low relative apertures such as f/1.5. Such lenses are costly to manufacture.